The present invention is related to a method of introducing an in situant into a vapor compression system, as well as to a method for detecting leaks in the system components and an apparatus and composition useful for leak detection. "In situants" are defined as compounds which are the same or substantially similar to compounds already present in oils or lubricants, and which exhibit fluorescence and/or daylight visible qualities.
Daylight visible and ultraviolet fluorescent dyes have been used to detect leaks in refrigeration systems utilizing fluorocarbon refrigerants and refrigerant oils. Typically, these dyes are introduced into the refrigeration system, and at the site of the leak, the leaking refrigerant, oil and dye are detected under normal or UV light. The term "dye" in the context of leak detection generally refers to a compound that is distinctively different or unintentionally similar to components in the host fluid, having the specific purpose of generating a detectable color from a fluid. Typical dyes used by the industry up to present include blue anilino-anthraquinones, xanthenes, perylenes, and naphthalimides.
More specifically, a leak-detecting trace fluid, which is generally a fluorescence (powdered) dye material dissolved in an oil or petroleum fraction carrier, is introduced into the refrigeration system. The fluorescent dye material is carried throughout the system, and at the location of a leak, the refrigerant, oil, and fluorescent dye material leak into the atmosphere. The refrigerant is subsequently vaporized, leaving an oil residue containing the fluorescent dye material. Application of a UV light to this area results in the illumination of the oil/fluorescent dye material. The primary factors in selecting these dyes for use in leak detection is that the dyes are soluble in the host fluid, and that the dyes are used in such low concentrations that their presence does not alter the intended normal function of the host fluid.
U.S. Pat. No. 1,915,965 discloses a leak detector method for a compression refrigeration system. Daylight visible compounds, such as methyl violet, crystal violet, auramine B, rhodamine E, etc. are added to such systems as leak detectors.
U.S. Pat. No. 4,249,412 discloses a UV fluorescent dye composition comprising water, a nonionic surfactant, a 1.0 wt. % sodium fluorescein and a semi-synthetic thickening agent. This fluorescent dye composition is sprayed on the external surfaces of a system where the bubbles formed by the leak fluoresce under UV light.
Other references include U.S. Pat. No. 4,369,120, which discloses anilino anthraquinone blue dyes (methyl-ethylanilino, dimethylanilino, and trimethylanilino anthraquinones) for use as visual leak detectors of refrigerants, refrigerant oils, and mixtures thereof; U.S. Pat. No. 4,758,366, which discloses a UV fluorescent dye composition comprising a polyhalogenated hydrocarbon refrigerant, a refrigeration oil, or a mixture thereof, with a fluorescent dye such as naphthoxanthenes, perylenes, or naphthalene; U.S. Pat. No. 5,149,453, which discloses a fluorescent dye composition comprising an effective amount of a fluorescent, alkyl substituted perylene dye combined with a refrigerant oil and a polyhalogenated hydrocarbon refrigerant; U.S. Pat. No. 5,357,782, which discloses a UV fluorescent dye composition comprising an optical naphthalimide brightener mixed with either mineral oil, polyalkylene glycol or polyol ester refrigeration lubricant; U.S. Pat. No. 5,167,140, which discloses a method of adding a fluorescent dye solution into a system with an atomizing mist infuser, wherein four different formulas for the fluorescent dye solution are disclosed, wherein the dye solution is a fluorescent dye mixed with an appropriate refrigerant oil; WO 92/07249, which discloses a method and a sensor system for detecting hydrocarbon-containing fluids by fluorescent detection, wherein additives typically used in hydrocarbon-based fluids, such as gasoline, heating oils and motor oils, can fluoresce, and can be used to detect and locate the source of ground water contamination from gasoline and oil storage tanks using a fluorescent sensor which detects the presence of fluorescing materials such as Coumarin 153. The use of Coumarin 153 in ppm concentrations for this purpose does not degrade the performance properties of the particular hydrocarbon or oil. Moreover, coumarin compounds are related in structure and derivation to anthraquinones, which are sometimes used to improve oxidation stability.
Furthermore, U.S. Pat. No. 5,440,919, discloses a method of introducing a UV fluorescent dye additive into a closed refrigeration system by placing the fluorescent dye on a swatch of material installed in a desiccant bag which is placed in a dehydrator or filter (i.e. filter-dryer) of the refrigeration system. The swatch is capable of releasing as well as adsorbing the dye. The refrigerant and system lubricant flow through the dehydrator and are then mixed with the fluorescent dye, thereby allowing the fluorescent dye to be carried throughout the system. Although this system allows the introduction of the fluorescent dye into the system without requiring the use of a carrier oil, it also requires that the dehydrator or filter-dryer of the system be changed in order to introduce the dye into the system.
U.S. Pat. No. 3,386,920 teaches the composition of a fluorescent and daylight visible dye dissolved in solvents such as alcohols and oils to detect surface defects by applying the solution to a surface containing the defect, wiping excess solution off of the surface, and allowing the solutions to exude from the defect for detection. This reference does not teach the advantages of using a carrier fluid or solvent which is compatible or soluble in the fluid used in the process for which the defect is located, nor is there any preference for using dyes which are in situants to the fluid located on either side of the wall wherein the defect is located. The compounds suggested for use by this reference include coumarins, dibenzothiophene, azole dyes, perylene dyes, and pyridotriazoles.
U.S. Pat. No. 4,201,683 teaches an anti-friction solution comprised of anti-friction compounds and C5-C50 alkanols added to equipment having moving parts operating under boundary lubricating conditions. This reference does not teach the method of introducing the solution to a system under pressure nor does it teach that these compounds could be selected from in situants in the system's oil or lubricant. This reference also does not teach that certain performance improving compounds exhibit fluorescent qualities which when added to the system can be used to detect leaks.
U.S. Pat. Nos. 4,157,970, 4,179,386, and 4,320,018 all teach compositions containing polyhydroxy anthraquinones for improving oxidation stability in lubricating fluids. Thus, polyhydroxy anthraquinones would be considered an in situant.
U.S. Pat. No. 4,641,518 teaches a method to detect surface defects by applying a solution comprised by one embodiment of 7-diethylamino-4-methylcoumarin in isopropanol, wiping away excess solution, and applying a developer solution to absorb the fluorescent dyes from the surface defect. This reference does not require or prefer any specific fluorescent dyes which are in situants to the system which is being analyzed for surface defects, nor are oils taught as the carrier fluid. A method to inject the fluorescent or dye solution into a pressurized system is also not taught. This patent also appears to be for finding defects on static surfaces in ambient by spreading the solution over large areas and then observing where the fluorescence emanates from. This is in contrast to the current invention whereby the in situant chemicals are used to detect leaks in flowing systems, as in the case of vapor compression refrigeration, and the outer surface at which the leak is detected does not need to be prepared or coated in any form prior to detecting for leaks.
U.S. Pat. No. 5,605,650 teaches a composition comprised of one or more fluorescent dyes in a volatile solvent for use in detecting tampering. This reference does not teach the use of oil carrier with preferred in situant fluorescent materials which are common to lubricants or oils used in a vapor compression system. Moreover, the specification that the carrier be volatile would not be applicable to the current invention since the leak detection method is facilitated by the concentrated presence of an in situant in the POE carrier and system oil after the refrigerant/system oil/carrier fluid/fluorescent compound solution leaks from the system and the refrigerant evaporates thereby concentrating the fluorescent in situant making its visibility improve with time.
Generally speaking, the standard industry method of introducing daylight visible or fluorescent dyes into a refrigerant oil, has been to dissolve the dye in the o refrigeration oil and to introduce this mixture into the system. There are however currently several different types of oils that are used in refrigeration systems. For example, polyalkylene glycol (PAG), polyol ester (POE), alkylbenzene (AB) and mineral oils are all used in current systems and some of these oils (or their additives) are incompatible with one another in concentrations as low as 1%. This means that a service technician must carry an inventory of all different types of fluorescent dye mixtures, i.e. one for each oil type.
An even greater problem with the conventional approach is that the technician must first determine which type of oil is used in the system which is being checked for leaks, as often, the technician is called upon to repair a leak in a system which has not been previously serviced and in which the oil used is unknown. This presents a significant problem. We have recognized that a more universal fluorescent leak check solution which is compatible with all potential lubricants and delivery method is needed to simplify leak detection in refrigeration systems.
The inventors have also taught the advantages of using an alcohol carrier fluid for leak detection (U.S. patent application Ser. No. 08/788,780). Namely, certain alcohols will dissolve daylight visible dyes and fluorescent compounds and are miscible with refrigerants and oils used in vapor compression refrigeration systems. This carrier can then be removed after functioning as a carrier for the dye or fluorescent agent.
The type of daylight visible or fluorescent material used for leak detection is also critical because the additives used in oils can interact with the material or the material could directly and negatively affect the properties of the oil or refrigerant. Although the quantity of material used for fluorescent leak detection is generally small, on the order of a few percent by weight of oil or less, a material can adversely affect the properties or performance of the oil or refrigerant to which it is added. The materials having fluorescence properties in accordance with the present invention are usually solid at room temperature, and are selected from a group of commercially available compounds, the same or substantially similar to those already used in the oil manufacturing industry as additives to promote the performance characteristics of oil. Many of these industry-added additive materials are also soluble in lubricants and oils, whether the oil is petroleum-derived (mineral) or synthetic but up until now their ability to fluoresce has not been appreciated.
The problems and disadvantages of current leak detection methods (i.e., introducing fluorescent and daylight-visible compounds using different carrier fluids for each type of oil) can be circumvented by replacing a part of or all of an alcohol carrier fluid with a POE (polyol ester) oil. POE oils are useful for this invention since they are generally universally miscible at low concentrations with other oils including AB, PAG, and mineral oils (whereas, AB, PAG, and mineral are not universally miscible in the other oils including POE) and POE oils can dissolve many fluorescent compounds and daylight visible dyes making POE oil an ideal carrier for administering the fluorescent or daylight-visible in situants into a refrigeration or lubrication system. The use of POE oil as a complete or partial replacement for an alcohol carrier fluid also does not require the additional step of removing the POE carrier fluid component by filtration after use as a carrier. Another advantage of using POE oil in solution with an alcohol as the carrier fluid is that the differences in chemical structure between POE oil and alcohols will allow for the dissolution of varying amounts of different fluorescent and daylight-visible in situants not possible with each component, alcohol or POE oil, alone. In other words, multi-component carriers allow for the possibility of more, and different, in situants to be added to the vapor compression system.
Another advantage of using POE oil as a carrier fluid is that many fluorescent or daylight-visible compounds, or families thereof, have equal or better solubility in POE oil compared to other oils, and similar solubilities compared to alcohols. For example, we have measured the solubility of the fluorescent compounds, N-phenyl-1-naphthylamine and N-phenyl-2-naphthylamine in two different POE oils to be 20-30% by wt. and about 5% by wt., respectively, whereas, the solubility in an AB and mineral oil is a factor of 3-10 lower. The solubility of the same in situants in alcohols are nearly the same at 20-30% and 1-6%, respectively.
Another drawback to current leak detection techniques is that conventional fluorescence leak detectors have used a very bright mercury vapor lamp with a UV filter. Commercial UV fluorescent leak detection devices also use halogen light sources. Other suitable UV light sources are disclosed Skoog, et al., Principles of Instrumental Analysis, Saunders College, 1980, Figure 5-2, p. 116, which lists components and materials for spectroscopic instruments and lists several light sources, including a xenon lamp, as a source of visible light.
Flashing UV light has been used for various applications in the past. Typically these applications use excited xenon in a light tube to provide continuous light or to provide UV energy for chemical curing reactions, such as in dental reconstruction. Up until our present invention, however, flashing UV light has not been recognized as beneficial for leak detection.
For example, U.S. Pat. No. 4,279,254 discloses a UV light used on medical patients to radiate the skin. The UV electrical light circuit, which is not battery operated, counts pulse flashes in order to automatically shut off and avoid over-exposure as a safety measure; U.S. Pat. No. 4,112,335 discloses a rapid pulse UV light apparatus in which a UV light source is fed as a high frequency pulse into a high pressure (3 atmosphere) xenon light tube to cure epoxy resin tooth caps; U.S. Pat. No. 4,550,275 discloses a high efficiency pulse light source as a xenon light source to excite lasers; U.S. Pat. No. 5,185,552 discloses a vacuum UV light source which provides a high output UV light source using low pressure hydrogen or deuterium in a hollow tube at wave lengths below 180 mm; U.S. Pat. No. 4,229,658 discloses a dental xenon light apparatus which supplies UV and visible light and is used to cure tooth restoration materials by focusing the light on a small area of a tooth; and U.S. Pat. No. 5,043,634 discloses a pulsed light source using a pulsed xenon light tube coupled with a phosphorus coating which emits different colors of visible light as a navigational aid.
Industries in which leak detection is important have not recognized that leaks can be detected by administering a fluorescing material to any system using a carrier fluid injected at any pressure, regardless of oil type, and detected using a UV lamp. It is also important to the present invention that the compounds being administered to the system for the purpose of providing the fluorescent or daylight-visible feature are, by themselves or by association with chemical families, improve certain properties of the oil or lubricant, and hence, these compounds or substantially chemically similar compounds are present in many oils or lubricants produced by oil and lubricant manufacturers. We define the term "in situants" to denote these compounds which are the same or substantially similar to those compounds already present in the oils or lubricants. We reserve the term "additive" to describe compounds added to a host fluid which are not identical or substantially similar to compounds already present in the host fluid. The compounds of the present invention are specifically chosen as in situants and should therefore not detrimentally impact the performance characteristics of the oil or lubricant, and in fact, these in situants may actually improve the properties of the oil or lubricant and at the same time provide the means to detect for leaks.
Moreover, we are not aware that anyone prior to our invention recognized that a daylight visible in situant can be used in addition to a UV fluorescing in situant to further facilitate visualization and location of leaks in vapor compression systems. Our recognitions provide a much simplified and advantageous method of leak detection.
An object of the present invention, is to provide a more effective method of introducing a fluorescent or daylight visible compound into a system to avoid the need for a system specific carrier oil and the time consuming process of replacing the filter to introduce the compounds.
Another object of the present invention is to provide a method of introducing an in situant into a system which will not degrade the performance of the system.
Another object of the present invention is to provide daylight visible or fluorescent in situants which are soluble in both the carrier fluid as well as the various types of refrigerant oils, i.e. synthetic or petroleum-derived. Solubility is desirable for at least two reasons. First, the in situant is dissolved in the carrier fluid alone for delivery into the refrigeration or air conditioning system. If the in situant were insoluble in the solvent, the in situant could precipitate or form a residue. As a result, inadequate amounts of in situant would be delivered into the system or insoluble residues could clog key system components, such as the expansion device, and cause operational problems. Second, once adequate amounts of the in situant are delivered into the system, the in situant must be soluble in the specific refrigerant lubricant used in the system, allowing the in situant to travel with the lubricant throughout the system to the location of the leak. The refrigerant/lubricant/in situant mixture then leaks into the atmosphere at the site of the leak, leaving a lubricant/in situant residue at the site which can be detected by visible light or by application of UV light to the area.
An objective of this invention is therefore to provide a carrier fluid which uses POE oil to replace some or all of an alcohol carrier fluid which is injected into a vapor compression system for leak detection.
Another object of this invention is to provide a method of introducing fluorescent or daylight-visible compounds, or mixtures thereof, into the oil or lubricant of a vapor compression system using a carrier solvent which need not be separated from the refrigerant oil or lubricant (system fluid) after its use as a carrier.
Yet another object of this invention is to provide a leak detection fluid which is comprised of fluorescent or daylight visible compounds already present as in situants in the systems oil or lubricant. In particular many fluorescent and daylight-visible dye compounds and families therefrom are used by oil and lubricant manufacturers as performance additives affecting anti-oxidation or anti-wear properties, for example, and the POE oil present in the carrier itself contains many additives to promote anti-oxidation, anti-wear, anti-corrosion, viscosity-improvements, and other performance factors.
Furthermore, another object of this invention is to provide a carrier fluid, comprised of POE oil or combinations of a POE oil and alcohol, which is soluble in all refrigeration oils or lubricants and which does not detrimentally affect the performance of the system.
Furthermore, another object of the present invention is to overcome the problems and disadvantages of conventional leak detecting light sources, which include power consumption and poor detection capabilities, by providing a high-efficiency xenon flashing light source. We have found that the advantage in using a flashing light instead of, for example, a continuous light source, is that it makes the fluorescing material more noticeable. That is, the flashing light provides the operator with a continuous comparison between a leaking region with fluorescence and the same region with normal ambient light, thereby making the fluorescing material appear to flash and easier to detect.
Normally, xenon lights inherently flash at a frequency so that the light is easily perceptible as continuous to the human eye. According to the present invention, however, the light has an adjustable on-off duty cycle, wherein the light may be off for 0.5 seconds or more. As a result of the longer off-time, such units use significantly less power and make battery powered units practical.
These objects have been achieved in accordance with the present invention by a method in which an in situant is introduced with a carrier fluid into a vapor compression system to detect system leaks.
The present invention also advantageously uses in situants with natural fluorescent characteristics which are not damaging to the performance of the oil, lubricant or refrigerant. Moreover, with the use of our invention and its general principles, the incorporation of certain in situants into the system actually benefits the performance, wear, stability, and/or life of the oil or lubricant when the in situant has anti-wear, anti-oxidant, viscosity improving, and/or dispersing properties.
According to the present invention, the extent to which the in situants are used is essentially only limited by the solubility of the in situant in the system fluid. The concentration of in situant should, generally speaking, be limited to an amount below which precipitation occurs, because precipitation of the in situant may be detrimental to the fluid system and performance.
Yet another advantage of the present invention is the use of mixtures of fluorescent materials and daylight visible in situants which, when used together, provide enhanced visual detection of the leakage and/or alter the fluorescent color of the fluorescent material to enhance detection of the mixture.
In accordance with the present invention, a method is utilizable by which an in situant and a fluid carrier can be introduced into a refrigerant system, regardless of the system pressure and temperature or whether the system is or is not open to the environment.
In summary, We have discovered that a carrier fluid comprised of POE oil, or POE oil in combination with one or more alcohols, preferably C1-C3 alcohols (i.e., methanol, ethanol, propanol), is an effective carrier by which to introduce in situants into a vapor compression system. Owing to the differences in chemical structure between alcohols and POE oils, there will also be fluorescent and daylight-visible in situants which are more or less soluble in each component, allowing more types and a larger number of in situant compounds to be incorporated into the combination carrier fluid. The properties of the POE, or POE-alcohol carrier fluid component are:
1. The carrier fluid must be miscible and compatible with AB, PAG mineral, and other POE oils; PA1 2. The in situants must be soluble in POE oil if the carrier fluid is comprised entirely of POE oil; PA1 3. The in situants must be soluble in POE and/or an alcohol if the carrier fluid is comprised of a POE oil/alcohol combination. PA1 1) POE oils are universally soluble in other oils and lubricants at low concentrations; PA1 2) No provisions need to be made for removing the POE carrier fluid component after its use as a carrier; PA1 3) In situants which are also fluorescent compounds or daylight-visible compounds, as well as those present in the POE oil, are administered to the system; PA1 4) Similar quantities of fluorescent or daylight-visible in situants, relative to those possible with alcohol carriers alone, can be added to a system since they are readily soluble in POE oil. Also, larger quantities of certain in situants can be added to a system using POE oil relative to other oils since these certain in situants have higher solubilities in POE oil. PA1 5) A larger diversity of fluorescent compounds or daylight-visible dyes or in situants can be added to a system since compounds can be selected which are soluble in alcohol or oil.
The benefits of using POE oil carrier fluid in this method for introducing fluorescent or daylight-visible in situants into the oil or lubricant of a vapor compression system are
Xenon tubes used as a light source according to the present invention, advantageously produce a full spectrum of light very efficiently, without the generation of significant heat. This light can then be filtered to remove the visible and IR frequencies, leaving only the ultraviolet spectrum. The result is an intermittent, intense light of long wave ultraviolet black light or UV-A, typically in the 180 nm to 390 nm wavelength range of the electromagnetic spectrum.
Generally, the light sources for detecting fluorescing materials require a filter to filter-out visible light. Without a filter, the illumination of the fluorescing material is much less noticeable. Typically, the filter is a glass filter because the conventional continuous light source generates sufficient heat to damage inexpensive filters. According to the present invention, however, the xenon filter cooling effect advantageously results from a duty cycle in which there is a relatively slow on/off frequency.
Xenon light sources are generally in the form of xenon arc lamps, which burn continuously, or xenon flash tubes which are typically flashed at very high frequencies to approximate (i.e., appear to the naked eye as) a continuous light source. However, the present invention employs a xenon light which is turned on at a low frequency, with a very pronounced on and off cycle. Such xenon flashing lights generate significantly less heat and thus avoid potential safety concerns, reduce fabrication costs, and allow for the use of inexpensive plastic or glass lenses or the application of a UV filter material directly on the xenon bulb. Their utilization in leak detection of the type involved herein provides advantages not heretofore recognized.
Instead of using a continuous beam of UV light, it was found that, by introducing an intermittent (on/off duty cycle) UV light, the UV sensitive fluorescing material is more noticeable. The on/off UV light source allows a repeated comparison between the fluorescing leak indicator and the background, much like a flashing warning light is more noticeable to a driver at night. We also found that an adjustable flashing frequency allows the user to adjust the frequency to suit the user according to ambient light conditions. The intermittent light also advantageously consumes significantly less power, making possible the use of- light-weight, low-cost, portable, battery-powered units.